Background Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by synovial hyperplasia, mononuclear cell infiltration, bone erosion and joint destruction. We have shown recently that a positive response of the seronegative RA patients to methotrexate therapy during 24 months of follow-up was associated with inhibition of the mechanistic target of rapamycin (MTOR) gene expression, which was accompanied by a significant decrease in the expression of inflammation markers and an absence of further bone destruction in these patients (1).

Objectives Here we hypothesized that MTOR inhibition by rapamycin (RAP) in cultured PBMCs obtained from RA patients might be associated with downregulation of genes responsible for bone resorption (MMP-9, cathepsin K), and inflammation (TNFα).

Methods Eight RA patients aged 53.4±10.8 years old, disease duration 8.2±7.1 years (with previous history of treatment with DMARDs) were examined. Control group consisted of 26 healthy subjects. PBMCs were fractionated on Ficoll density gradient and cultured with 1 nM rapamycin during 48h. Cell viability was monitored by 0.2% Trypan blue staining. Total RNA isolated from these cells was used for MMP-9, cathepsin K, and TNFα gene expression studies performed with quantitative Real-time RT-PCR.

Results At baseline gene expression of MTOR, MMP-9, cathepsin K, and TNFα measured in the PBMCs was significantly upregulated (p<0.05) in the examined RA patients compared to healthy subjects. Significant downregulation of MTOR gene expression in response to RAP treatment of the PBMCs in three of the examined patients compared to the untreated cells was associated with significant inhibition of pro-inflammatory cytokine TNFα and the joint destruction-related MMP-9 and cathepsin K gene expression. The absence of RAP effect on MTOR gene expression in the PBMCs of other examined patients compared to untreated counterparts was accompanied by no change in gene expression of the examined pro-inflammatory mediator and genes associated with bone turnover.

Conclusions Coordinate downregulation of MTOR, pro-inflammatory cytokine, and markers of bone destruction in the cultured PBMCs from RA patients in response to rapamycin treatment points to MTOR signaling pathway involvement in the inflammation and joint destruction associated with RA.

References

1. Tchetina EV, Demidova NV, Karateev DE, Nasonov EL. Rheumatoid Factor Positivity Is Associated with Increased Joint Destruction and Upregulation of Matrix Metalloproteinase 9 and Cathepsin K Gene Expression in the Peripheral Blood in Rheumatoid Arthritic Patients Treated with Methotrexate. Int J Rheumatol, 2013; 2013:45787

Acknowledgements This study was funded by Russian Foundation for Basic Research (project no. 12-04-00038-a to EVT).

Disclosure of Interest None declared